Acquired resistance to chemotherapeutic agents is a major problem in cancer treatment. Anthracyclines are an important class of drugs to which acquired resistance is often observed. We have identified a panel of anthracycline resistant human tumor cell lines and selected one - the doxorubicin resistant fibrosarcoma HT1080/DR - for analysis by molecular biological techniques. This cell line is of particular interest because it fails to express the P-glycoprotein gene and yet has a multiple drug resistant phenotype. Genes which are differentially expressed between HT1080/DR and the sensitive parental cells will be identified by subtractive cloning and cDNA expression techniques. These genes will be related to the drug resistant phenotype of HT1080/DR by several tests including the use of mammalian expression vector constructs. Identification of non-P-glycoprotein dependent mechanisms of anthracycline resistance will be important in defining the complete spectrum of potential mechanisms of acquired drug resistance in the clinical setting.